1. Field of the Invention
This invention relates to an on-vehicle navigation apparatus indicating a map on a changeable scale. In addition, this invention relates to a computer program for controlling the indication of a map to change the scale of the indicated map. Furthermore, this invention relates to an navigation method to provide the indication of a map on a changeable scale.
2. Description of the Related Art
A general on-vehicle navigation apparatus includes a display device of a liquid crystal type or a CRT type which indicates a two-dimensional or three-dimensional map showing the current position of the vehicle, a desired destination, and a selected or recommended route to the destination. A user can input information about the destination into the navigation apparatus via voices uttered or via a digitizer. The navigation apparatus may give audible guidance on the route.
A first advanced on-vehicle navigation apparatus indicates a small-scale map of a large area to simultaneously show the current vehicle's position, a desired destination, and a recommended route to the destination when the current vehicle's position is far from the destination. The first advanced apparatus indicates a large-scale map of a small area when the current vehicle's position is near the destination.
A second advanced on-vehicle navigation apparatus changes an indicated-map scale depending on whether or not the current vehicle's position is near an intersection at which the vehicle should turn. Specifically, the second advanced apparatus indicates a detailed large-scale map of a small area to clearly show a required portion of a recommended route to a desired destination when the current vehicle's position is near an intersection at which the vehicle should turn.
Generally, important points on which guidance should be given in vehicle navigation are referred to as maneuver points. The maneuver points include a crossing or an intersection at which the vehicle should turn, a landmark, and a dangerous point for which a warning should be given. The maneuver points are also called the guide points.
There are prior-art technologies for changing the scale of a map indicated in a navigation apparatus.
Japanese patent application publication number 07-332993/1995 discloses an on-vehicle navigation apparatus which indicates a map showing the current vehicle's position. The apparatus of Japanese application 07-332993 is designed to automatically change the display scale of the indicated map in response to movement of the current vehicle's position to provide proper navigation information to the vehicle's driver.
In the apparatus of Japanese application 07-332993, a map database is searched for a recommended route to a desired destination. Detection is made as to important points such as a right/left-turn crossing and a complexly-shaped crossing in the recommended route. When the current vehicle's position approaches an important point, a desired map scale is set on which both the current vehicle's position and the important point are simultaneously in a same display screen. The map is drawn and indicated on the desired scale, and both the current vehicle's position and the important point are simultaneously shown in the indicated map. Thus, when the current vehicle's position approaches an important point, a detailed large-scale map of a small area is indicated. On the other hand, when the current vehicle's position is far from important points, a small-scale map of a large area is indicated. Accordingly, in the case where the vehicle continuously moves along a succession of important points, a small-scale map of a large area remains unindicated for a long time. In this case, it tends to be difficult for the vehicle's driver to accurately grasp the relation among the current vehicle's position, the recommended route, and the destination.
Japanese patent application publication number 2001-74481 discloses an on-vehicle navigation apparatus which indicates a map on such a scale that both a starting point and a desired destination are simultaneously shown in the indicated map. When the user traces a desired rough route to the destination on the indicated map by use of a user's finger or a pen in contact with a display surface, information about the desired rough route is inputted into the apparatus. A recommended detailed route close to the desired rough route is searched for. The recommended detailed route is shown in the indicated map. In the case where the starting point is far from the destination, a detailed large-scale map of a small area can not be indicated even when the vehicle approaches an important point such as a crossing.
Japanese patent application publication number 2002-148058 discloses an on-vehicle navigation apparatus designed so that the scale of an indicated map and the number of important points shown in the indicated map are in a predetermined relation. The important points are, for example, intersections, interchanges, junctions, service areas, and parking areas.
In the apparatus of Japanese application 2002-148058, a display surface can be divided into first and second windows. The first window is occupied by an indicated map inclusive of important points while the second window is occupied by a list of the names of the important points. The number of important points to be shown can be controllably designated by the user. The scale of the indicated map is decided in accordance with the designated number of important points to be shown. Thus, the scale of the indicated map is varied as the designated number of important points to be shown is changed.
In the apparatus of Japanese application 2002-148058, the scale of the indicated map is controlled so that the indicated map will be the most detailed in a range where it can simultaneously show both the current vehicle's position and a desired destination. Accordingly, a more detailed map is indicated as the vehicle moves toward the destination. In the case where the current vehicle's position is far from the destination, a detailed large-scale map of a small area can not be indicated even when the vehicle approaches an important point.